The goal of this project is to determine the three-dimensional structure of the Fab' fragment of a human myeloma immunoglobulin to atomic resolution by X-ray diffraction single crystal techniques. The amino acid sequence will be established by chemical analysis and will be used to help in the interpretation of the electron density map. Complexes between various ligands and the Fab crystals will also be studied by X-ray diffraction to provide a model of hapten-antibody interactions.